High blood pressure is a significant factor behind potentially fatal conditions such as heart attacks and strokes. But a new study has found that higher intake of flavanols, a family of polyphenolic compounds found in fruits, vegetables and wine, is associated with lower blood pressure in men and women.
Past research has found evidence of a link between red-wine compounds and lower blood pressure, but the new study, published in Scientific Reports, adds more weight to the hypothesis by specifically investigating one particular compound and its impact on health and by measuring study participants' flavanol levels directly, rather than relying solely on diet questionnaires. The research was conducted by scientists at the University of Reading, Cambridge University and the University of California at Davis. (The study was partially funded by a grant from Mars, Inc., a food company.)
Nutritionist and lead author Dr. Gunter Kuhnle and his team focused on flavan-3-ol, one of the six classes of polyphenolic compounds commonly found in Western diets. They analyzed data from the Norfolk cohort of the European Prospective Investigation into Cancer Study (EPIC), a large study that tracked diet and health information of more than 25,000 participants over the course of 20 years. Participants were recruited between 1993 and 1997, and were between the ages of 40 and 75. The study compiled data from self-reported food frequency questionnaires and tracked changes in systolic and diastolic blood pressure.
What makes this study different from past efforts is the use of nutritional biomarkers. Rather than rely solely on the self-reported questionnaires, Kuhnle and his team also looked at blood and urine test results that measured flavanol intake. The high variability of flavanols in certain foods made the biomarkers essential. While a participant could report drinking one glass of wine per day, one glass of wine could contain the same amount of flavanols as three glasses of a different wine.
"Wine can have a lot of flavanols, but that again depends on the variety and vintage," Kuhnle told Wine Spectator. "There are some reds with very low content and whites with much higher content, so it's not straightforward." That made measuring biomarkers more crucial.
The results showed that high flavan-3-ol intake, specifically from tea, wine and apples, was associated with lower blood pressure. Kuhnle's threshold for hypertension was 140 mm Hg (millimeter of mercury) for systolic blood pressure and 90 mm Hg for diastolic blood pressure. Male participants in the top 10 percent of flavan-3-ol consumption had a systolic blood pressure that was 2 mm Hg lower than those in the bottom 10 percent. Women in the top 10 percent had a systolic blood pressure that was 2.5 mm Hg lower than those in the bottom 10 percent. That reduction is comparable to the long-term effects of the Mediterranean diet.
Additionally, the effect of high flavan-3-ol intake on blood pressure was strongest among those already suffering from hypertension. "The association between intake and blood pressure therefore follows a progressive model, where the strongest effect size is found in those with higher blood pressure," Kuhnle writes.
Unfortunately, the EPIC study recorded only one urine sample per participant. Multiple samples would have provided a better estimation of habitual intake of flavanols. "The main caveat of our study is that we had to rely on a single measurement," Kuhnle said. "It would of course have been great to have more over several years to investigate longer term effects."